We have studies the II-VI ternary compound semiconductor ZnSe grown by molecular beam epitaxy ¡]MBE¡^Method. The modulation spectroscopy was used to study ZnSe. ZnSe epilayer was grown on GaAs substrate. The lattice mismatch¡]0.27 ¢H¡^between GaAs and ZnSe create a strain at the GaAs/ZnSe interface. The strain will remove the degeneracy of heavy and light holes to conduction band transition energies. We use the photoreflectance to measure the energy of different thickness ZnSe epilayers at low temperature. It was found that as the epilayer thickness becomes larger, the£GE will become smaller. We have also analyzed the energy of different temperatures in terms of Varshni relation, and the temperature dependence of the broadening parameters.